In clinical practice, mobile X-ray imaging systems are used in cases, where patients are unable to leave the patient's bed and where it may become necessary to conduct medical imaging diagnostics in bedside situations. Such mobile X-ray imaging units can comprise a movable X-ray base unit, which may further be equipped with further functions and applications, such as image processing or control functions. For example, a movable base unit can further comprise a support arm, where an X-ray tube is mounted to.
A separate detector or detector panel receives the radiation, which has irradiated, for instance, a region of interest of a patient. The detector converts the detected radiation to electrical signals and can provide this image information to the base unit and the processing unit, for instance, via wireless or wired data connection. For the acquisition of an X-ray image, it can be important to adjust and align the X-ray tube and the detector at an optimal distance, a right angle, and correctly centered relative to each other. Especially, when additionally using an anti-scatter-grid, the grid and the tube have to be well aligned to avoid unwanted grid artefacts. Different technical approaches have been proposed to achieve a proper alignment of X-ray source and detector. U.S. Pat. No. 7,736,055 B2 describes an optical detection of deviations from an optimal arrangement using light reflectors at the detector, which reflect light transmitted by a light source arranged near the X-ray source. However, the practical usability of such arrangement solutions in clinical practice can often be very limited.
WO 2013/080111 A1, only relevant for novelty, discloses an X-ray imaging system comprises an X-ray tube, a ceiling suspension for the X-ray tube, a detector trolley with an X-ray detector mounted thereon, an active sensor matrix, an optical indication unit and a control unit. The active sensor matrix is fixedly mounted on the ceiling suspension, the optical indication unit is fixedly mounted to the detector trolley and is adapted for emitting an optical indication onto the active sensor matrix. WO 2011/141763 A1 discloses an apparatus for obtaining an intraoral x-ray image from a patient with an x-ray source and an intraoral image detector comprising one or more detectable elements. One or more sensors are positionally coupled near the x-ray source and are energizable to sense the location of the one or more detectable elements when the intraoral image detector is within the patient's mouth.